Inductive probe



Oct. 31, 1967 H. STRAUCH 3,350,670

QINDUCTIVE PROBE Filed Dec. 21L, 1964 2 Sheets-Sheet 1 Fig.1

I nvenlor H. Straucfi Attorneys H. STRAUCH INDUCTIVE PROBE Filed Dec. 21, 1964 2 Sheets$heet 2 I Inventor hf Strauch United States Patent '2 Claims. (Cl. 336- 90) The present invention relates to an inductive probe and more particularly to a construction of inductive probe which can 'be produced in sub-miniature form and which is capable of operating at hightemperature.

From one aspect the invention provides an inductive probe comprising a core consisting of a bundle of wires, at least one coil extending around saidcore, part of the length of the wires of thecore being bent back over the outer surface of said at least one coil and an outer layer of insulating material extending around the coil and core assembly. Preferably, the core is made of a ferromagnetic wire having a high permeability, for example, soft iron wire.

In a preferred construction, the bundle of wires forming the core, pass through apertures in two spacer members which are spaced apart to accommodate at least one coil between them them. However, where the probe comprises more than one coil, more than two spacer members may be provided which are arranged along the core so as to define spaces in each of which one or more coils is located.

The invention also provides a method of constructing an inductive probe which comprises forming a bundle of wires into a core, fitting the wires through a bore provided in at least two spacer members which are spaced apart along the core, disposing at least one coil around the core in the space or each space between the space members, bending back a part of the, length of the wires of the core over the outer surface of the spacer members and the at least one coil and providing an outer layer of insulating material around the'coil and core assembly.

The probe may be completed by providing terminal means for making external electrical connections to the coil or coils and it may alsobe provided with a holder by means of which the probe may be mounted.

In order that the invention may be more fully understood, reference will now be made to the accompanying drawings, in which: i

FIGURE 1 shows one stage during the manufacture of one embodiment of inductive probe according to this invention,

FIGURE 2 is a sectional view showing a further stage during the manufacture,

FIGURE 3 shows a completed probe, also partly in section,

FIGURE 4 is a sectional view showing one stage during the manufacture of a further embodiment of inductive probe,

FIGURE 5 shows a further stage during the manufacture of this embodiment, and

FIGURE 6 shows the complete probe.

Referring to FIGURES 1 to 3 of the drawings, the core generally indicated at 1, consists of a bundle of ferromagnetic wires 2 which are coated with a high temperature lacquer or resin to electrically insulate the wires from each other, the number of wires in the bundle being chosen to give the required cross-section area of the core. The core is generally of'circular cross-section.

Alternatively the wires may be oxidised to give them an insulating coating by heating them in an atmosphere of oxygen. This method also serves to anneal the wires and so remove any work-hardening present or imparted to the wires due to cutting to lengths to form the bundle.

The bundle of wires is pushed through holes 3, in two spacer members 4, 5 which are made of a high temperature insulating material, such as an epoxy resin, Tufnol (trademark) or ceramic, and which are spaced apart to provide a gap 6 within which a coil 7 can be wound and to form end cheeks for the coil. The length of the gap and the wall thickness of the end cheeks are dimensioned.

to provide the required space for the coil. If desired, the spacer members may be fixed to the bundle of wires forming the core by a high temperature resin and the coil 7 is then wound in the gap between the spacer members. The coil is wound from ahigh temperature insulated wire and as it. is wound, the wire may, if required, be passed through a high temperature liquid resin which serves to bond the turns of the coil :to each other as well as to the core and to the spacer members. The portion 2a of the bundle of wires extending beyond the spacer member 5 is bent backwards over the outer surface of the coil and the spacer members, as seen in FIGURE}, so that they are fairly equallydistributed .around this outer surface." This assembly is then inserted into a sleeve 8 of high temperature insulating material, for example glass fibre filled nylon, in which it is a push fit. The ends 7a of'the coilare soldered or spot welded to connector members 9 fixed in the end 8a of the sleeve 8.

The probe is filled preferably under vacuum, with a high temperature epoxy resin. When this resin is set, the end of the probe is machinedolf at a point along its length as indicated at A--A, depending upon the core length required. If desired the probe maybe fixed in a holder 10 by means of which it can be mounted in a desired position. i

Referring now to the embodiment shown in FIGURES 4 to 6, the probe generally comprises similar parts to the previous embodiment, namely'a core 1 consisting of a bundle of ferromagnetic wires 2 on which are mounted two spacer members 4 and 5 which are separated along the core so as to define a space in-which is wound a coil 7. As in the previous embodiment, the portion. 2a of the bundle of wires extending beyond'the spacer member 5 is bent backwards over the outer surface of the coil and spacer members. In order to facilitate the equal distribution of the bent back portions of the wires over the outer surface, the assembly is mounted ma jig 11 (FIGURE 4) having a flange 11a provided with equally spaced radially extending slots 12 in which the individual wires are located and pulled tight. Two slotted washers 13 and a clamp ring 14 held by a resilient clip 15 are then fitted over the wires so as to urge'them into close engagement with the outer surface of the assembly.

In this embodiment'the connector member for making external electrical connection to the leads of the coil comprises a small printed circuit panel 16 which is fitted over and adhesively secured to the end of the spacer member 5 and provided with two printed circuit contact areas 17 to which the ends of the coil are respectively soldered. The slots in the washers 13 enable them to be slipped over the panel 16, whereafter the washers are rotated so that the slots are out of line. The washers 13 and clamp ring 14 can then be pushed towards the jig 11 to tauten the wires 2a over the surface of the spacer member 4.

The jig 11 and washers 13 can now be removed leaving the wires 21: held by the clamp ring 14.

The assembly thus formed is then placed in a mould 18, as shown in FIGURE 5 so that the probe assembly is located in the mould cavity 18a and the clamp ring 14 forms a plug for the mould. The mould is filled with an epoxy resin such as Araldite (trademark). The mould and resin mix are degassed in vacuo prior to pouring of the resin which is subsequently cured. Thus the resin, when set, forms the outer layer of insulating material 19 (FIG- URE 6) around the coil and core assembly as well as penetrating to the interior of the assembly. After removal from the mould, the clamp ring-is removed and the end of the assembly adjacent thereto is cut or machined off to provide a probe having the core length required, as is shown in FIGURE 6. As in the previous embodiment, the probe may be fixed in a holder by means of which it can be mounted in a desired position. One embodiment of probe constructed in accordance with the method shown in FIGURES 4 to 6 has an overall length of approximately 0.43 inch and an overall diameter of approximately 0.25 inch.

The inductive probe according to this invention, has reduced parallel eddy current losses due to the use of small diameter ferromagnetic wire with a high permeability to form the core. It enables a high carrier frequency to be used so giving a high frequency response for inductance changes of the probe. The gap and the core length can be easily constructed to give good linearity and sensitivity when the probe is used to detect small armature movements, i.e. as an inductance with a variable air gap. The probe can be used under conditions of high temperature, for example up to about 150 C. where an epoxy resin is employed. 7

By using ceramics for the spacer members and filling the probe assembly with a high temperature glaze, as well as winding the coil from a resistance wire such as Nichrome (trademark) or a glass insulated wire it is possible to construct an inductive probe according to this invention which can be used at temperatures up to about 600 C.

It will be understood that various modifications may be made Without departing from the scope of this invention. Thus, if desired, the coil or coils incorporated in the probe can be prewound for assembly on the bundle of wires forming the core. Moreover instead of using the slotted washers 13, clamp ring 14 and resilient clip 15, a rubber O ring can be used to tauten the wires on the spacer member 4.

I claim:

1. An inductive probe capable of working at high frequencies and withstanding a temperature of at least 150 0., comprising:

a a core consisting of a bundle of ferromagnetic wires,

at least one coil extending around said core,

a first spacer member extending around said core on one side of said coil,

a second spacer member extending around said core on the other side of said coil,

part of the length of said wires of the core being bent back around the outer surface of said first spacer member, and extending over the outer surface of said coil and the outer surface of said second spacer member,

said second spacer member serving to space the coil from one end of the probe by a desired amount,

an outer layer extending around the assembly of the coil, core and spacer members, and

terminal means adjacent said first spacer member and extending axially of said probe for making electrical connections to said at least one coil.

2. An inductive probe capable of working at high frequencies and withstanding a temperature of at least 0., comprising:

a core consisting of a bundle of ferromagnetic wires,

at least one coil extending around said core,

a first insulating spacer member extending round said core on one side of said coil and spaced from either end of said bundle of wires,

a second insulating spacer member extending around said core on the other side of said coil and extending between said coil and one end of said bundle of wires,

part of the length of the wires of the core being bent back around the outer surface of said first spacer member and extending over the outer surface of said coil and the outer surface of said second spacer member so that the other end of said bundle of wires, is coplanar with said one end of said bundle of wires and separated therefrom by said spacer member,

said second spacer member also serving to space the coil from one end of the probe by a desired amount,

an outer layer extending around the assembly of the coil, the core and the spacer members, and,

terminal means adjacent said first spacer member and extending axially of said probe for making electrical connections to said at least one coil.

References Cited UNITED STATES PATENTS 619,760 2/1899 Kinraide 336-234 X 819,268 5/1906 Doman 336234 X 1,597,901 8/1926 Kent 33696 X 2,962,679 11/ 1960 Stratton 33683 FOREIGN PATENTS 352,251 4/ 1922 Germany. 260,731 11/1926 Great Britain.

LARAMIE E. ASKIN, Primary Examiner.

C. TORRES, T. J. KOZMA, Assistant Examiners. 

1. AN INDUCTIVE PROBE CAPABLE OF WORKING AT HIGH FREQUENCIES AND WITHSTANDING A TEMPERATURE OF AT LEAST 150* C., COMPRISING: A CORE CONSISTING OF A BUNDLE OF FERROMAGNETIC WIRES, AT LEAST ONE COIL EXTENDING AROUND SAID CORE ON A FIRST SPACED MEMBER EXTENDING AROUND SAID CORE ON ONE SIDE OF SAID COIL, A SECOND SPACER MEMBER EXTENDING AROUND SAID CORE ON THE OTHER SIDE OF SAID COIL, PART OF THE LENGTH OF SAID WIRES OF THE CORE BEING BENT BACK AROUND THE OUTER SURFACE OF SAID FIRST SPACER MEMBER, AND EXTENDING OVER THE OUTER SURFACE OF SAID COIL AND THE OUTER SURFACE OF SAID SECOND SPACER MEMBER, SAID SECOND SPACER MEMBER SERVING TO SPACE THE COIL FROM ONE END OF THE PROBE BY A DESIRED AMOUNT, AN OUTER LAYER EXTENDING AROUND THE ASSEMBLY OF THE COIL, CORE AND SPACER MEMBERS, AND TERMINAL MEANS ADJACENT SAID FIRST SPACER MEMBER AND EXTENDING AXIALLY OF SAID PROBE FOR MAKING ELECTRICAL CONNECTIONS TO SAID AT LEAST ONE COIL. 